Superregenerative receiver quenching circuit



Ddi. 17, 1.946. I v W, E, BRADLEY 2,412,710

SUPERREGENERATIVE RECEIVER QUENCHING CIRCUIT Filed July 15, 1944 Patented Dec. 17, 1946 SUPERREGENERATIVE RECEIVER QUENCHING CIRCUIT William E. Bradley, Swarthmore, Pa., assignor to" Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania V j, I

Application July 15, 1944, Serial No; 545,077 1 5 claims. (cl. 25o-2o) The present invention relates to superregenerative receivers, and more particularly to an improved superregenerative receiver Iadapted for operation at high and ultra-high radio frequencies.

` A superregenerative receiver may be characterized briey as comprising a highly regenerative amplifier circuit in combination with a quenching means for alternately making the said circuit oscillatory and non-oscillatory, usually at a superaudible frequency rate. Although the superregenerative circuithas not been widely used in the pa-st, it nds fimportant application in certain specic instances, particularly at very high carrier frequencies, where great amplification is desired with a minimum of tubes, expense, and equipment.

I VThe present invention is particularly directed to an improved method of, and apparatus for, quenching the oscillating circuit of `a superregenerative receiver. While the said method and apparatus is applicable to superregenerative receivers generally, it i-s particularly useful where very high quenching frequencies, e. g. of the order of a megacycle or more, are to be employed. Quenching frequencies of this magnitude are used, for example, where it is desired to employ a superregenerative receiver in the reception of radar or radar-beacon signals. Such signals are commonly time-spaced pulses transmitted in the form of a series of ultra-high frequency pulse signals (interrupted continuous Waves). A typical system may use pulses of one or two microseconds duration, occurring at a repetition rate of 50'0 to 1000 per second, and modulated on an ultra-high frequency carrier Wave. Manifestly, where the individual pulses have a duration of only a microsecond, it would be impractical to employ superregenerative receivers utilizing quenching frequencies of less than a megacycle, since otherwise many of the received pulses might go undetected.

When superregenerative receivers employing very high quenching frequencies were rst constructed, a serious problem, which had not previ- Ously been met, was encountered. It was found that when a very high quenching frequency was employed, it was impossible, by conventional quenching methods, to insure adequate quenching in the brief intervals between the oscillatory periods of the superregenerative circuit. It was soon evident, however, that, at the end of each quenching interval, it is highly important that no ysubstantial carrier oscillation (preferably n ot even a microvolt) be present in the tank circuit of the quenched oscillator. If such oscillations,

2 y hang-overs from the previous oscillatory period, be present, they cause the sensitivity of the receiver to vary with incomingL carrier signal fre,- quency. In suchI circumstances the Areceivers sen-sitivity vs. frequency characteristic exhibits a series of peaks separated, along the frequency axis, by distances equal to the quenching frequency. Since such a characteristic is undesirable, it is important that complete quenching be attained in each quenching interval.

.Prior to the conception of the present invention itA Was'known that reasonably complete quenching, with very high quenchingfrequencies, could be effectedby employing a high impedancalow Q tank circuit, i. e. 'aftank circuit Whose decrement, or self-damping factor, 'was very high. This was not considered a satisfactory solution to the quenching problem, however, because of the inefciencies introduced by the low Q tank circuit.

Accordingly, in orderto provide anadequate quenching arrangement, the presentdnvention utilizes a special damping means which functions only `during the quenching interval and hence doesnot deleteriously affect the operation of the receiver during theoscillatory period. I 1

It is, therefore, an object of the present invention. `to provide an `improved superregenerative receiver for operation at. high and ultra-high radio frequencies.` H

It is another objectof the present invention to provide an improved superregenerative receiver capable of eiiiciently receiving high frequency pulse signals of short duration. I It is still another object of the present invention to `provide an improved superregenerative receiver adapted for operation with very high quenchingirequencies.

It is another object of the present invention to provide an improved superregenerativ'e detector circuit having a lowimpedance high Q tank circuit. ,l I

It is still another object of the present invention toprovide an improvedarrangement for quenching a -superregenerative receiver capable of operating in the ultra-high frequency region. .I

These, and` other objects` will subsequently become apparent 'by reference to the following description taken in connection with the accompanying drawingwherein the single figure shows aI circuit diagram of a superregenerati've receiver constructed n accordance with thepresent invention. I

Reference may now be had tothe improved superregenerative receiver circuit shown schematically in the drawing; Basically, this circuit com4 circuit, is in part conventional, and will be recog-V nized as the well known Colpitts arrangement. The oscillator` includes, however, a novel grid biasing arrangement which greatly improves the performance of the oscillator, per se, and the eificiency and stability of the superregenerative system in general.

the eifect of the electrode capacities) distant from the grid and plate electrodes of the triode I 0. A tap connection I8 may be provided on the line conductor I3 to serve as means for coupling a suitable antenna to the resonant tank circuit.

In accordance with the present invention, and vinorder to insure complete vand rapiddamping in each quenching interval, there is'provided an electronic damping element 4, conveniently a diode, Whose electrodes are connected across the open end of the resonant line 2. As shown in the drawing, the anode I9 should be connected to the grounded line conductor I3, while the cathode '415 This novel grid biasing ar- '5 rangement, is fully described and claimed -in my co-pending application Serial No. 545,078, filedI July 15, 1944.

Briefly, this biasing arrangement comprises a v,compound grid leak and condenser circuit consisting of a first leak and condenser combination 6-7 of long time constant and a second leak vand condenser combination 8 9 of short time constant. Preferably the latter time constant is less than the time constant of the resonant -line 2, While the first-mentioned time constant is greater than the maximum period of the vmodulation signals vto be received. The grid coupling condenser 9 is preferably small, e. g.

of the order of the inter-electrode capacitances `of the oscillator tube I Il. If desired, a small, selfresonant choke II may be provided in series with the resistors 6 and 8, as explained in the above-mentioned co-pending application. detector circuit 5 is also described in the said lco`pending application.

The oscillator tank circuit 2 consists of a Vresonant transmission line comprising parallel conductors I2 and I3 'The line 2 is preferably somewhat shorter than a half wave-length, so that its effective length as modified by the sevferal terminating tube capacities, is substantially Ya half wavelength.` The connections between the grid and plate electrodes of the triode I0 and the 1 l tank circuit 2 are conventional. The cathode of triode I3 may be connected to ground through a suitable RF choke I4.

A direct current source of plate voltage may be provided for the oscillator tube l0, if desired, lbut it is preferred to omit this, and to derive the necessary plate power from the square wave generator 3 which functions, .in a manner well known inthe art, both as an external or separate quenching voltage source and as a plate power source. `Although reference is here made to the generator 3 as a square wave generator, it will be understood, of course, that the specific wave shape employed is not a critical factor, and consequently the present invention is vnot to be I construed as limited to the use of any specific .wave form.

'Aradio frequency choke coil l5 is preferably included in the connection-between the high voltage terminal of the square wave generator 3 and the anode circuit of triode l0. Where the high voltage plate source 3 iszconnected to the anode'of tube I0 by way of one of the conductors of the resonant fline 2, it is preferred that the `connection I6 be made at the point of minimum RF potentialon .the line conductor I2. The point I1 of minimum RF potential on the other line conductor I3 mayv be -connected to 'ground as shown.` .In general, 'the' points I6' and I'I will be an .electrical quarter' -:wave length 4(including 23 4should b'e connected to the high voltage line conductor I2. During the oscillatory period, i. e. the period when the high voltage positive 1-alternation of the square wave generator 3 is applied to the line conductor I2, the diode 4 is non-conductive, since its cathode 20 is highly positive with respect to its anode I2. When the diode is thus'non-con'ductive, it constitutes only a small capacitance across the open end of the line 2, and it has only a negligible effect on the starting time of the oscillator. However, during the negative alternations of the voltage supplied by the square wave generator 3, the diode 4 is highly conductive, and hence it :constitutes a relatively low impedanceV short circuit across the right-hand end of the line. If the characteristic impedance of the line i2 is of the order of the internal impedance of the diode 4, 'the diode will have a very powerful quenchingor damping action. Under these conditions the diode will absorb oscillations very quickly.y Where the impedance match between the diode and the line is perfect the quenching or damping is complete after one cycle of the carrier signal. In practice it has been found that lines having characteristic impedances of the order of 500 ohms yield very satisfactory results in combination with diode vstructures presently available.

Although the present invention has been described with particular reference to the single embodiment of the drawing, it will be understood that the invention is capable of various forms of physical expression, and consequently is not limited to the specific disclosure, but only by the scope of the appended claims.

I claim: l l. In a superregenerative radio receiver, the combination comprising an oscillator tube having at least a grid, a cathode, and an anode, a resonant tank circuit comprising a segment of trans'- mis'sion line whose length'is of the order of a half wave length of the carrier signal to be received, a source of alternating voltage having its terminals connected across said transmission line at a point of low radio frequencypotential, said source functioning during odd half-cycles as a source of plate potential lforsa'id tube and during even halfcycles as a separate oscillation quenching means, and a diode connected across saidr transmission line at a pointof high radio frequency potential, said diode being so connected that itacts as a short circuit 'on .said linev only :during the' said even half-cycles.v f 2. In a superregenerative radio receiver, the combination comprising a' reso-nant .line whose electrical lengthis' `somewhat'less than Ja half Wave length at" the operating frequency, 'anlos'cilelator tube coupled to oneend of lsaidlinefa' diode connected across the other end of saldline, said line, modified by the shunt capacities of said oscilI lator tube and saidfdiode, being effectively an electricalhalf wave .length longfat said operating fre'- quency, and a source of alternating voltage connected across said line at a point intermediate the ends thereof.

3.*In a superregenerative radio receiver, the combination comprising a resonant line Whose length is of the order of a half Wave length at the operating frequency, said resonant line consisting of a first line conductor and a second line conductor, an oscillator tube having its anode coupled to one end of said first conductor and its grid coupled to the corresponding end of said second conductor, a diode having its cathode connected to the other end of said first conductor and its anode connected to the corresponding end of said second conductor, and a source of alternating voltage connected across said line at a point near the electrical center thereof, said source serving alternately as a source of oscillator plate voltage and as a source of oscillator quenching voltage.

4. In a superregenerative radio receiver, the combination comprising a resonant line, an oscillator tube coupled to one end of said line, said line serving as a tank circuit for said tube, damping means comprising a diode connected to the other end of said line, and a source of alternating voltage connected across said resonant line at a point intermediate the ends thereof, said source serving during positive voltage alternations as a source of plate current for said oscillator tube, and serving during negative oscillations to render said diode conductive, whereby rapidly to damp the electrical oscillations established in said tank circuit during said positive alternations.

5. In a superregenerative radio receiver, the

combination comprising a resonant line Whose electrical length is somewhat less than a half Wave-length at the operating frequency, an oscillator tube coupled to one end of said line, said line serving as a tank circuit for said tube, a diode connected across the other end of said line, the internal impedance of said diode being approximately equal to the characteristic impedance of said line, said line as modied by the presence of said oscillator tube and said diode being eiectively an electrical half Wave-length long at said operating frequency, and a source of alternating voltage connected across said resonant line :at a point Whchi electrically is substantially one-quarter wave-length from either end thereof, said source serving during positive voltage alternations as a source of plate current lfor said oscillator tube, and serving during negative oscillations to render said diode conductive, whereby rapidly to damp the electrical oscillations established in said tank circuit during said positive alternations.

WILLIAM E. BRADLEY. 

